This invention relates to calibration adjustment of electromagnetic fuel injectors which are utilized in conjunction with two and four cycle spark ignited internal combustion engines. The fuel injectors contemplated here are designed for direct cylinder injection and are intended to operate in the general range of about 100-1500 psi or perhaps lower, as in throttle body injection, but not in the very high diesel injection ranges which may be as high as 10,000 psi.
The development of practical electronic fuel injection systems in recent years has led to a plethora of fuel injector devices designed to provide maximum engine performance. Several of the known devices are disclosed in U.S. Pat. Nos. 3,450,353, 4,040,569 and 4,164,326.
It is important for the injectors to work in harmony with their respective engines, and this requires that the injectors be suitably calibrated to provide the desired fuel volume and time-of-flow for each injection into the engine.
It is an object of the invention to provide a fuel injection concept which permits simplification of calibration procedures over the known devices. It is a further object to provide the ability to easily perform such procedures on a bench-mounted injector prior to installation of the injector on an engine. It is yet another object to provide for coarse as well as fine adjustments to optimize the injector-engine performance. An additional object is to eliminate the need for disconnecting the fuel line from the injector during part of the bench calibration process.
The calibration of fuel injectors can be made in relation to an "injector flow characteristic curve" which plots, for any given injection, the fuel volume vs. the time the injector discharge port is open (commonly called the "pulse width"). See SAE Technical Paper No. 800164, Feb. 25-29, 1980. Proper calibration should be made, taking into account both the slope and position of the curve, which is normally linear.
In accordance with the various aspects of the invention, a fuel injector includes a housing having fuel upstream inlet and downstream discharge end portions. The discharge end portion is adapted to adjustably receive a valve assembly. The valve assembly, in turn, includes a valve poppet, seat and biasing primary compression spring arrangement which is adjustable prior to the assembly's insertion into the injector housing. The inlet end portion of the housing includes the usual magnetic coil and an armature which forms a working gap with the housing. The armature is attached to an actuator which engages the valve assembly. A biasing secondary compression spring is confined between the armature and an upstream fuel inlet member adjustably mounted to the housing.
Three adjustments are contemplated for the device. The first or preload adjustment is to the compression of the primary spring in the valve assembly, which is subsequently inserted into the housing. The second adjustment is between the valve assembly and housing, which positions the valve seat as well as setting the upstream working gap. This modifies the slope of the injector flow characteristic curve. The third adjustment is made between the upstream fuel inlet member and the housing, which preloads the compression of the secondary spring and offsets the position of the injector flow characteristic curve, as desired.
An additional aspect of the invention contemplates the provision of a device associated with the upstream fuel inlet for making the appropriate third adjustment during fuel flow through the injector. In the disclosed embodiment, a calibration device includes a cap which is fit over the fuel inlet and is provided with a fuel inlet port. A slotted tool extends into the cap and engages a corresponding slot in the fuel inlet member in a manner so that fuel can flow through the joint therebetween. Manipulation of the tool adjusts the fuel inlet member relative to the housing while fuel is flowing through the cap and into the injector.